[FIX] Check the next base pointer for possible invariant loads

  A load can only be invariant if its base pointer is invariant too. To
  this end, we check if the base pointer is defined inside the region or
  outside. In the former case we recursively check if we can (and
  therefore will) hoist the base pointer too. Only if that happends we
  can hoist the load.

llvm-svn: 260886